The Program Project continues to focus on cardiac electrophysiology and cardiac contractility investigations with the long-term goal of achieving a good physiological understanding of cardiac electrical and mechanical events and thereby provide useful and new diagnostic methods. To this end, the work is carried out by a tightly knit group of investigators from varied disciplines including physicians, physiologists, engineers, physicists, and computer scientists. In the electrophysiology studies, major emphasis is projected for studies on: 1) the inverse calculation of the epicardial potential distribution from body surface maps in patients and animals, and 2) the development of two- and three-dimensional physiological and mathematical models of propagation plus the cardiac electrical field of excitation waves and of ventricular repolarization. With these methods our objective is to develop improved ways to obtain new knowledge about the origin and perpetuation of arrhythmias and to understand the origin of body surface potentials in abnormal cardiac states. The ultimate goal of the cardiac muscle mechanics studies is to obtain a complete description of the changes in cardiac contractility in normal and in abnormal states, to understand their origin at the sarcomere level, as well as to evaluate their manifestations in the intact heart in humans. This aim will be pursued through three types of studies: those in the intact heart of animals and patients with respect to force frequency characterization of contractility, in vitro studies on whole muscle with respect to how length, rate, and pattern of stimulation and environmental conditions combine to determine overall contractility, and those that require a study of the contractile element itself to determine the basic mechanical properties of the sarcomere.